The present invention relates to arteriovenous grafts and methods for implanting the same. It relates in various embodiments to an arteriovenous graft that has a stepped down venous end, an arteriovenous graft having a cuff for attachment to a target vein and methods relating thereto that include inserting the venous end of a graft into the target vein for positioning downstream of the venotomy site.
Approximately 40,000 new patients per year begin hemodialysis. This number continues to rise annually at a rate of about 10 percent. It has been reported that creation and maintenance of hemodialysis access accounted for approximately $800 million in physician and hospital expenditures in 1998. The term xe2x80x9caccessxe2x80x9d identifies a location within a patient""s circulatory system that is specifically configured to act as a site for supplying blood to a dialysis machine and for receiving blood returning from a dialysis machine. Preferred modes of access, if the patient""s condition allows, are grafts or fistulas, each of which is a subcutaneous device in fluid communication with the patient""s circulatory system into which needles can be repeatedly inserted for transferring blood to and from a dialysis machine during dialysis treatments.
The most common cause of a hospital admission for dialysis patients is an access-related problem, and the cost and frustration of access failure is expected to continue to rise until a solution to the current access problem is identified and instituted. Even in view of this great need, no major advances in hemodialysis access have occurred in the last 30 years. Hakim and Himmelfarb, in their article entitled xe2x80x9cHemodialysis Access Failure: A Call to Action,xe2x80x9d concluded by saying, xe2x80x9cas far as [hemodialysis] access, we can no longer continue doing the same thing (very little indeed), the same way..., and expect that the lives of our [end stage renal disease] patients will be better or that the cost of access care will diminish.xe2x80x9d Hakim R, Himmelfarb J. Hemodialysis Access Failure: A Call to Action, Kidney International Vol 54, (1998), pp. 1029-1040. If the patency rate of an access could be doubled, hundreds of millions of dollars would be saved annually and could be in turn directed toward transplant programs or a cure for renal disease. In addition, dialysis patients, particularly patients suffering from end stage renal disease (xe2x80x9cESRDxe2x80x9d), would then be able to enjoy more productive, healthy and happy lives.
A primary arteriovenous fistula (AVF) is the preferred and most cost-effective long-term access for hemodialysis patients. An AVF is an artificial direct connection between an artery and a vein. High blood flow through this connection causes the vein to become much larger and develop a thicker wall, more like an artery. The AVF thus provides a high blood-flow site for accessing the circulatory system for performing hemodialysis. For each dialysis, two large-bore needles (normally 14-16 gauge) are inserted through the dialysis patient""s skin and into the AVF, one on the xe2x80x9carterialxe2x80x9d end and the other on the xe2x80x9cvenousxe2x80x9d end. When the tips of the needles are properly resting inside the access, a column of blood enters the end of tubing attached to each needle. Prior to beginning a dialysis treatment, a cap is removed from each tubing, thereby allowing blood to fill the tubing, and then a syringe of saline is injected through each tubing and needle. The two needles are then connected with rubber tubing to the inflow (arterial) and outflow (venous) lines of the dialysis machine, and dialysis is started.
Unfortunately, even with careful physical examination and/or the use of doppler ultrasound or venography to identify suitable veins, it has been reported that approximately 40-50% of patients do not have the vascular anatomy sufficient to create a primary AVF. In addition, many dialysis veterans, for whom the use of an AVF has previously failed, can no longer be considered candidates for a primary fistula.
The next option for long-term access is the placement of an arteriovenous graft (xe2x80x9cAVGxe2x80x9d). An AVG is a length of plastic tube, usually made of porous polytetrafluoroethylene (xe2x80x9cPTFExe2x80x9d), which is surgically placed under the skin, fluidly connecting an artery and a vein. Once a graft is placed, a dialysis machine can be fluidly connected to the patient""s circulatory system by inserting needles into the graft and connecting the needles to the dialysis machine with tubing as described generally above in connection with an AVF. The phrase xe2x80x9clong-term access,xe2x80x9d however, is a misnomer when discussing an AVG, because reported patency rates are very low, with one-year patency rates of only 40% frequently reported. Even with graft surveillance and aggressive prophylactic measures to prevent thrombosis, primary and secondary patency rates remain low; and the additional costs incurred are also thought to be unreasonably high.
Although many factors have a role in the limited durability of PTFE grafts, enemy number one is the progressive development of neointimal hyperplasia (NIH) with venous anastomotic narrowing and subsequent graft thrombosis. Thrombosed grafts can be declotted surgically or percutaneously, or elaborate atherectomy devices, angioplasties, or stenting procedures can be utilized; but still, the NIH will predictably recur. A revision of the graft with a more proximal anastomosis can also be completed but this too has been found to be very susceptible to failure. There is a great need to improve the patency rates of AVGs to decrease cost and improve patient quality of life.
Neointimal hyperplasia is thought to occur because of many factors, including, for example, injury to endothelium with release of growth factors, turbulent flow at the anastomotic site, vibratory forces on the anastomosis, shear forces, uremia, and other hypothetical etiologies. A multitude of studies show the persistent and consistent development of NIH at the venous anastomotic site.
Physicians have used stepped and tapered grafts, which typically have a gradually increasing diameter along a portion of the graft or along the entire length of the graft from the arterial end to the venous end, and which terminate at the venous end with an opening at a point having the greatest diameter of the graft. An example of a tapered graft having a continuously increasing diameter is set forth in FIG. 1, wherein the diameter of the lumen at venous end 1 is larger than the diameter at the arterial end 2.
A general belief that has become widespread among medical practitioners is that the development of NIH could be prevented or delayed by increasing the size of the venous anastomosis. In an attempt to improve AVG durability, xe2x80x9chooded graftsxe2x80x9d with a large venous anastomosis have been utilized. A representative example of a prior art hooded graft (Venaflo, Impra Company) is set forth in FIG. 2, wherein the venous end 3 has a xe2x80x9choodxe2x80x9d configuration. However, no significant improvement has been reported resulting from the use of such a hooded graft. Indeed, the Venaflo graft has been found in some cases to occlude sooner than a standard stepped graft. Furthermore, attempts to salvage the graft by surgical or nonsurgical thrombectomy have been found to be more difficult to accomplish and have been found to result in comparatively shorter secondary patency rates.
In view of the above, there is a great need for alternative modes of treatment and care of hemodialysis patients. In particular, a great need exists for new hemodialysis access grafts and methods for surgically placing the same. These needs are addressed by the present invention.
The present invention addresses problems associated with hemodialysis access grafts known in the prior art by providing novel grafts and methods for surgically placing the same. The embodiments of the invention exhibit a variety of excellent features.
One form of the present invention is a unique arteriovenous graft having a stepped down venous end. The venous end can include a section of generally constant diameter that is adjacent a stepped section of increasing diameter, which is in turn adjacent a section of a larger generally constant diameter. Alternatively, the stepped section can begin at the venous end and have an increasing diameter to an adjacent section of larger diameter. The stepped section can vary in length and slope, and can provide a generally linear increase in diameter or a nonlinear increase. Another form of the invention is an arteriovenous graft that also has a stepped down arterial end.
Another form is a unique arteriovenous graft having a cuff positioned a preselected distance from the venous end for attachment to the wall of a target vein. The cuff defines a groove for receiving a purse-string suture in the vein wall. The cuff can be a single unit affixed to the exterior surface of the graft or can include a plurality of units. In one embodiment, the cuff comprises two rings about the circumference of the graft at a preselected position that are spaced from one another to provide a groove therebetween for receiving the suture and vein wall.
Another form of the invention includes a method for implanting an arteriovenous graft that includes making an incision (venotomy) in the wall of a target vein, inserting the venous end of an inventive graft into the vein such that the venous end is positioned downstream of the venotomy site, and securing the graft to the vein wall. In an embodiment in which a cuffed graft is used, the securing includes making a purse-string suture that engages the groove of the cuff.
It is one object of the invention to provide novel arteriovenous grafts and methods for implanting the same that provide an alternative to the unsatisfactory grafts and methods of the prior art.